Lenovo ServeRaid-8s PCIe 39R8812 Compatible Battery 3.7V 1800mAh

Lenovo ServeRaid-8s PCIe — 3.7V Li-ion Replacement Battery (39R8812)

This 3.7V 1800mAh Li-ion cell replaces the OEM battery on the Lenovo ServeRaid-8s PCIe RAID controller. It provides backup power to the controller's cache memory during unexpected power loss, protecting buffered write data until the system recovers. Voltage and capacity match the 39R8812 / 25R8118 OEM specification.

• ServeRaid-8s PCIe compatibility: The 8s PCIe controller uses a dedicated BBU slot tied to a specific voltage rail and BMS handshake. This cell meets that voltage threshold, so the controller recognises the unit and transitions its BBU status correctly.
• Bench tested on actual hardware: We cycled this cell through charge, rest, and discharge on a BBU load fixture. The BMS accepted the cell without throwing a fault code, and charge termination occurred at the expected voltage ceiling.
• Learn cycle initiation after swap: After fitting this battery, trigger a BBU learn cycle from your management interface — StorCLI: /cx bbu show and then initiate recalibration. The controller holds write-through mode until the learn cycle completes and recalculates the backup window against the new cell's actual capacity.

RAID controller staying in write-through mode after battery swap

The ServeRaid-8s PCIe does not automatically switch to write-back mode when a new battery is installed. It waits for the BBU learn cycle to complete and confirm the cell can sustain the backup window threshold. Until that cycle runs, the controller treats the battery as uncalibrated and keeps caching disabled. On Broadcom/LSI-based controllers, run StorCLI /c0 bbu startlearning to kick off the process — it typically takes 24 to 72 hours under normal server load.

Management console showing a battery fault days after installation

The ServeRaid-8s PCIe runs its battery self-assessment on a timed schedule, not at boot. If the console flags a battery error two or three days after the swap, the scheduled assessment ran before the learn cycle had finished recalibrating the new cell. This is not a fault with the replacement cell itself. Let the learn cycle complete fully, then check the BBU status again — a healthy cell reads above 3.6V at rest with charge status showing "Optimal" in the controller log.